New radiopharmaceuticals suitable for labeling with 99mTc will be synthesized using the bifunctional chelates iminodiacetic acid and ethylenediamine diacetic acid (EDDA). Organ distribution, urinary excretions and plasma clearance of these labeled compounds will be carried out in laboratory animals, to select the specific agent which is extracted with the highest efficiency by the renal tubular cells, for use eventually as a diagnostic agent in man, using the scintillation camera. The organ distribution of commonly used renal radiopharmaceuticals such as I131 - orthoiodohippurate, Tc99m glucoheptonate, dimercaptosuccinate, DTPA and In113m-DTPA will be determined at various time intervals to enable a more accurate estimation of the radiation doses resulting from their administration. The efficiency of renal imaging with Tc99m glucoheptonate and a high resolution scintillation camera will be compared with that of intravenous urography and nephrotomography in the detection of long-standing pyelonephritis. The diagnostic value of radioisotopically labeled leukocytes for the early detection of rejection will be explored in dogs with renal transplants, and the results compared with conventional renal radiopharmaceuticals.